Age-related changes in mastication.

The paper reviews human mastication, focusing on its age-related changes. The first part describes mastication adaptation in young healthy individuals. Adaptation to obtain a food bolus ready to be swallowed relies on variations in number of cycles, muscle strength and volume of emitted saliva. As a result, the food bolus displays granulometric and rheological properties, the values of which are maintained within the adaptive range of deglutition. The second part concerns healthy ageing. Some mastication parameters are slightly modified by age, but ageing itself does not impair mastication, as the adaptation possibilities remain operant. The third part reports on very aged subjects, who display frequent systemic or local diseases. Local and/or general diseases such as tooth loss, salivary defect, or motor impairment are then indistinguishably superimposed on the effects of very old age. The resulting impaired function increases the risk of aspiration and choking. Lastly, the consequences for eating behaviour and nutrition are evoked.

Tongue-mandible coupling movements during saliva swallowing.

The purpose of this study was to measure the tongue and mandible positions and displacements in relation to the maxilla in the midsagittal plane to characterize the different saliva swallowing patterns by recording their kinematics. A 2D electromagnetic articulograph using four transducer coils, three attached to the upper surface of the tongue midline plus one attached to the chin anterior part allowed continuous evaluation of tongue and chin movements in twelve young adults in good general health. During 170 s sequences recorded at a frequency of 100 Hz, subjects were at rest, silently reading a text they had chosen. The subjects were free to swallow during the sequence. Deglutition of accumulated saliva was analysed after averaging all values obtained during successive 250 ms periods. We identified three elementary swallowing patterns. Mean duration of tongue-mandible movements were 1·51 ± 0·17 s, 1·63 ± 0·14 s and 2·00 ± 0·08 s for the first, second and third patterns respectively. In the light of other studies based on intra-oral pressure recordings, our results help to understand the tongue-mandible coupling behaviours involved in managing an in-mouth saliva bolus during the three elementary swallowing patterns identified.

Mood-induced variations of mandible and tongue postures.

Twelve young adults in a good general health were observed during habitual posture of tongue and jaw in different emotional conditions induced by watching three video sequences. The position of the mandible was tracked by the displacements of an electromagnetic sensor glued to the chin. The tongue-to-palate distance was obtained by 2-D location of three electromagnetic sensors placed on the tongue upper midline surface. Head displacements were evaluated with a sensor fixed to an upper central incisor and were subtracted from corresponding displacements of tongue and chin sensors to obtain the real tongue and mandible positions during continuous recording sequences. Emotional conditioning by a fear movie influenced the vertical position of the mandible: the mean interarch distances during the fear movie (2·34 ± 0·24 mm) were significantly different from those measured during the tender (3·13 ± 0·35) and neutral (3·42 ± 0·80) movies, respectively (anova repeated measure, SNK; P < 0·05). anova repeated measure indicated that the tongue-to-palate distance differed significantly when the subjects were watching the conditioning movies (P = 0·003), the tip of the tongue taking a lower position during the fear movie than during the tender and neutral movies.

Substantiation of an artificial saliva formulated for use in a masticatory apparatus.

The aim of this work was to substantiate artificial saliva prepared for use in a masticator apparatus. Mastication's goal is to produce a viscous and plastic food bolus where these properties authorize a safe swallow. Apart from its biochemical contribution, saliva is mainly used in this kind of apparatus to provide a viscous component to the bolus. Artificial saliva was prepared with water and minerals, and completed with mucin and amylase. Different physico-chemical conditions were applied and the resultant viscosity was compared to that of human saliva. Mechanically- or chemically-stimulated salivas of ten healthy subjects were collected. Viscosity was measured with a capillary viscometer in response to changes in measurement's temperature, air exposure or pH. The effects of circadian saliva collection and the stimulation type on viscosity of human saliva were also studied. Viscosity of artificial and human salivas was comparable. An increase in the measurement's temperature or a 30 min-exposure of saliva to air led to a significant decrease in viscosity of both types of saliva. Amylase in artificial saliva did not change viscosity. The viscosity of human saliva displayed important subject variability as well as a dependence on the stimulation type of saliva production. This work allowed a useful evaluation of the formulated artificial saliva. It exhibited similar viscosity as the natural saliva in response to different methodological conditions. Therefore the proposed artificial saliva satisfies the major requirement of viscosity for a use in the masticator apparatus designed to prepare a food bolus.

Deciphering the protein digestion of meat products for the elderly by in vitro food oral processing and gastric dynamic digestion, peptidome analysis and modeling.

The elderly population will increase sharply in the future, along with an emerging range of specific nutritional needs that include adapted food. We aimed to develop a workflow to study the fate of a food, objectify the bioavailability of nutrients in the case of the digestive physiology of the elderly, and model the fate of proteins in the stomach. Pork frankfurters were subjected to in vitro normal and deficient mastication and gastric digestion, mimicking adult and elderly food oral and digestive processing. Swallowable food boluses were characterized for granulometric and rheological properties. Biochemical analyses were conducted on the bolus and on the digesta. Macronutrients, label-free peptide quantification and identification were performed, and modeling was applied to protein digestion kinetics. After deficient mastication, the food bolus was harder with more large particles, lower free iron release and more protein oxidation. The amount of peptides released in the stomach progressively increased, but to a lower extent for the elderly digestive condition and irrespective of masticatory efficiency. 592 peptides were identified from 67 proteins. Different trajectories were observed for adult and elderly digestive conditions, and two groups of meat proteins were identified based on the rate of hydrolysis. Designing suitable foods requires in vitro tools to evaluate the possible benefit for the elderly. Besides the well-known notion of Food Oral Processing (FOP), our work broadens the concept by extending oral activity to digestion when working in a nutritional context. This new concept is named Food Oral and Digestive Processing, FODP.

Reduction of low grade inflammation restores blunting of postprandial muscle anabolism and limits sarcopenia in old rats.

Ageing is characterized by a decline in muscle mass that could be explained by a defect in the regulation of postprandial muscle protein metabolism. Indeed, the stimulatory effect of food intake on protein synthesis and its inhibitory effect on proteolysis is blunted in old muscles from both animals and humans. Recently, low grade inflammation has been suspected to be one of the factors responsible for the decreased sensitivity of muscle protein metabolism to food intake. This study was undertaken to examine the effect of long-term prevention of low grade inflammation on muscle protein metabolism during ageing. Old rats (20 months of age) were separated into two groups: a control group and a group (IBU) in which low grade inflammation had been reduced with a non-steroidal anti inflammatory drug (ibuprofen). After 5 months of treatment, inflammatory markers and cytokine levels were significantly improved in treated old rats when compared with the controls: -22.3% fibrinogen, -54.2% alpha2-macroglobulin, +12.6% albumin, -59.6% IL(6) and -45.9% IL(1beta) levels. As expected, food intake had no effect on muscle protein synthesis or muscle proteolysis in controls whereas it significantly increased muscle protein synthesis by 24.8% and significantly decreased proteolysis in IBU rats. The restoration of muscle protein anabolism at the postprandial state by controlling the development of low grade inflammation in old rats significantly decreased muscle mass loss between 20 and 25 months of age. In conclusion, the observations made in this study have identified low grade inflammation as an important target for pharmacological, nutritional and lifestyle interventions that aim to limit sarcopenia and muscle weakness in the rapidly growing elderly population in Europe and North America.

Potentially modifiable determinants of malnutrition in older adults: A systematic review.

BACKGROUND & AIMS: Malnutrition in older adults results in significant personal, social, and economic burden. To combat this complex, multifactorial issue, evidence-based knowledge is needed on the modifiable determinants of malnutrition. Systematic reviews of prospective studies are lacking in this area; therefore, the aim of this systematic review was to investigate the modifiable determinants of malnutrition in older adults. METHODS: A systematic approach was taken to conduct this review. Eight databases were searched. Prospective cohort studies with participants of a mean age of 65 years or over were included. Studies were required to measure at least one determinant at baseline and malnutrition as outcome at follow-up. Study quality was assessed using a modified version of the Quality in Prognosis Studies (QUIPS) tool. Pooling of data in a meta-analysis was not possible therefore the findings of each study were synthesized narratively. A descriptive synthesis of studies was used to present results due the heterogeneity of population source and setting, definitions of determinants and outcomes. Consistency of findings was assessed using the schema: strong evidence, moderate evidence, low evidence, and conflicting evidence. RESULTS: Twenty-three studies were included in the final review. Thirty potentially modifiable determinants across seven domains (oral, psychosocial, medication and care, health, physical function, lifestyle, eating) were included. The majority of studies had a high risk of bias and were of a low quality. There is moderate evidence that hospitalisation, eating dependency, poor self-perceived health, poor physical function and poor appetite are determinants of malnutrition. Moderate evidence suggests that chewing difficulties, mouth pain, gum issues co-morbidity, visual and hearing impairments, smoking status, alcohol consumption and physical activity levels, complaints about taste of food and specific nutrient intake are not determinants of malnutrition. There is low evidence that loss of interest in life, access to meals and wheels, and modified texture diets are determinants of malnutrition. Furthermore, there is low evidence that psychological distress, anxiety, loneliness, access to transport and wellbeing, hunger and thirst are not determinants of malnutrition. There appears to be conflicting evidence that dental status, swallowing, cognitive function, depression, residential status, medication intake and/or polypharmacy, constipation, periodontal disease are determinants of malnutrition. CONCLUSION: There are multiple potentially modifiable determinants of malnutrition however strong robust evidence is lacking for the majority of determinants. Better prospective cohort studies are required. With an increasingly ageing population, targeting modifiable factors will be crucial to the effective treatment and prevention of malnutrition.

Oral declines and mastication deficiencies cause alteration of food bolus properties.

In the elderly, masticatory function often presents failure in certain oral tasks due to impairment such as decline in muscular force, jaw or tongue motility, neuro-muscular coordination, tooth damage, malocclusion and saliva production. Great disparity is observed in the various and potentially cumulative oral declines that occur with ageing. Such difficulties may have an impact on food consumption and nutritional status. To obtain better understanding of the consequences of several oral deficiencies, a series of swallowable boluses were prepared in vitro with the AM2 masticator apparatus with normal and deficient programming. Physiological normal mastication (NM) was simulated using in vivo data from healthy subjects. Chewing deficiencies were reproduced by alteration of NM programming to perform different levels and combinations of force loss, lack of saliva and decrease in the motility of oral elements. Poultry meatballs were used as test-food. Particle size distribution in the food bolus was measured by sieving and rheological features (hardness, cohesiveness and elasticity) were assessed with a TPA test. Compared to the NM outcome, significant and gradual deterioration of the food bolus was observed and associated with alteration in force, saliva and motility. Combinations of several failures led to greater or cumulative deficiencies in swallowable bolus properties. For the elderly presenting a high prevalence of various oral injuries, tailoring textured food cannot be ignored as a solution for remedying deficiencies and favoring the formation of a safe-swallowable bolus, which is an essential vector of nutrients. Knowing the impacts of oral injuries on the food bolus is obviously a requisite for developing diet strategies, including nutritional items for specific populations.

Mastication of model products in complete denture wearers.

OBJECTIVE: The aim of this study was to define the characteristics of muscular activity in complete denture wearers and in dentate subjects during mastication of model foods differing in hardness but similar in terms of rheologically properties. MATERIAL AND METHODS: The foodstuffs used in this study were laboratory-developed gumdrops demonstrating viscoelastic properties. The test foods cover a range of four hardness levels. The group of complete denture wearers included 15 subjects, while the control group included 9 subjects with normal dentition. Electromyograph (EMG) recordings were taken from the masseter and temporal muscles during mastication of the test foods. The results were evaluated by one-way and two-way ANOVA followed by means comparisons using a Student-Newman-Keuls post hoc test (alpha=0.05). RESULTS: Preparing the same food bolus for swallowing required a greater number of masticatory cycles and a longer duration of mastication for complete denture wearers than for dentate subjects. In addition, complete denture wearers failed to increase EMG activity per cycle in response to hardness of the food. CONCLUSION: Denture wearers experienced difficulties during mastication, as indicated by a decreased masticatory rate and the observed failure to increase EMG activity per cycle in response to increased food hardness. The increases in number of cycle and masticatory duration appear to be a response to this impaired masticatory function.

Adaptation of healthy mastication to factors pertaining to the individual or to the food.

Mastication is a physiological process controlled by the central nervous system and modulated by inputs from the mouth. Both the intrinsic characteristics of the subject and the extrinsic characteristics of the chewed food are responsible for variations of the masticatory function. Age, gender and dental state constitute the most studied intrinsic factors whereas hardness, rheological characteristics such as plasticity or elasticity, and food size are the better known extrinsic factors. These factors cause physiological adaptations which can occur during individual cycles or the whole sequence of mastication. Electromyographic and jaw movements (kinematic) recordings are commonly used to study mastication, from which, several variables can be measured. Vertical and lateral amplitudes and, velocities of jaw movements, are only given by kinematic recordings. Bioelectrical activities per cycle or per sequence are closely linked to masticatory forces and are measured from electromyographic recordings. Number of cycles, sequence duration and masticatory frequency can be measured from both types of recordings. The objective of this review is to provide an overview of the variations of the measured masticatory variables that occur when mastication adapts to changes in characteristics of the individual or the food.

Protective effects of taurine on human hair follicle grown in vitro.

Taurine is a naturally occurring beta-amino acid produced by methionine and cysteine metabolism. It is involved in a variety of physiological functions, including immunomodulatory and antifibrotic. Taking advantage of the ability of human hair follicle grown in vitro to recapitulate most of the characteristic features of normal hair follicle in vivo, we studied (i) taurine uptake by isolated human hair follicles; (ii) its effects on hair growth and survival rate; and (iii) its protective potential against transforming growth factor (TGF)-beta1, an inhibitor of in vitro hair growth and a master switch of fibrotic program. We showed that taurine was taken up by the connective tissue sheath, proximal outer root sheath and hair bulb, promoted hair survival in vitro and prevented TGF-beta1-induced deleterious effects on hair follicle.

Stabilization of mandibular complete dentures by four mini implants: Impact on masticatory function.

OBJECTIVES: The frequent instability of mandibular removable complete dentures causes an alteration of mastication. An innovative therapeutic strategy involves placing four symphyseal mini implants. This study aimed at assessing the development of masticatory parameters and the impact on quality of life in subjects that underwent this procedure. METHODS: Eleven edentulous subjects (mean age 72±11 years) with unstable mandibular complete dentures were followed-up before (T0) and two - three months after (T1) mini implant setting. Physiological parameters (number of cycles, duration of sequence and frequency of mastication) during the mastication of food models and the bolus median particle size (d50) of carrot were evaluated at each time. Quality of life was assessed at T0 and T1 using the Global Oral Health Assessment Index (GOHAI). Parametric tests were used to test relationships between mastication, quality of life variations and mini implant setting, and to compare each parameter mean value at times T0 and T1. RESULTS: More subjects were able to chew carrot after setting the mini implants (8 subjects compared to 4 at T0). This improvement was accompanied by changes in kinematic parameters when chewing carrots, soft and hard model food, and by an improvement of their quality of life. However, the particle size values observed in the bolus remained higher than for normal dentate subjects (9.2±2.8mm). CONCLUSIONS: These results indicated that the placement of mini implants as retentive elements for mandibular full dentures had a positive impact on patients' masticatory function and quality of life. CLINICAL SIGNIFICANCE: The placement of mini implants has a positive impact on the masticatory function and oral health quality of life. The results suggest that this alternative procedure can be used as a treatment option for patients unable to receive conventional implants.

Influence of bitter taste on mastication pattern.

Mastication is a rhythmic activity that can be modified by peripheral information generated in the mouth. To study whether taste cognition could influence the way in which a food is broken down in the mouth, subjects masticated firm, sugar-based gelatine gels with differing concentrations of quinine, up to 1500 micromol/kg, while electromyography (EMG) of masticatory muscles was recorded. Taste intensity and composition of saliva were measured. With increasing quinine concentration, the average number of chews for nine subjects decreased from 30 to 22, and their average clearance time increased from 7 to 14 sec. Quinine concentration had no effect on chewing frequency (1.3 Hz) or on the rate of salivation (5.5 g/min). Bitterness increased, while acceptability and sweetness decreased, with increasing concentration of quinine in the gel and in saliva. Taste cognition could therefore modify food breakdown in the mouth.

Clinical evaluation of mastication: validation of video versus electromyography.

BACKGROUNDS AND AIMS: The ability to evaluate masticatory function in people with neurological disabilities is important as this function is often compromised in these groups. However, current standard techniques are often impossible in such groups due to cognitive difficulties. This study is a validation of several variables read from standardised video recordings of mastication as indicators of masticatory function. METHODS: Fifteen healthy, fully dentate male subjects were recorded using EMG and by video simultaneously. An evaluation was undertaken of the video parameters (i) to compare their validity against the electromyographic parameters, (ii) to test intra-rater and inter-rater reliability and (iii) to test the ability to discriminate between four model foods differing in hardness. RESULTS: Masticatory time and the number of masticatory cycles counted on video were found to be valid and reliable indicators. In addition, the number of active chewing cycles performed with an open mouth and identification of the chewing side, were found to have reasonable validity and reliability. The former may allow discrimination between food types. CONCLUSION: As an alternative to the complex evaluation of masticatory function, observation of certain parameters from video recording could be an alternative for use in uncooperative patients.

Particle size distribution of food boluses after mastication of six natural foods.

There is a large variability between and among individuals in the physiology of mastication, but it is not known whether this produces a similar variability in the particle sizes of food boluses at the end of the chewing process. Food boluses obtained just before swallowing were analyzed in ten subjects (aged 36.7 +/- 9.5 yrs) with normal dentition. Food samples of 3 nuts (peanut, almond, pistachio) and 3 vegetables (cauliflower, radish, and carrot) were chewed and expectorated after self-estimated complete mastication. Measurements with sieving and laser diffraction methods indicated that particles were much larger in vegetables than in nuts. Particle size distributions were similar among nuts and among vegetables. Surprisingly, no inter-individual variability was observed in the particle distributions for the 6 foods, although several sequence variables differed markedly. A need for a bolus to be prepared with a precisely determined texture before it can be swallowed may explain the inter-subject variability of the masticatory function.

Effects of food texture and sample thickness on mandibular movement and hardness assessment during biting in man.

This study was designed to investigate the relationship among jaw movements, physical characteristics of food, and sensory perception of hardness in man. Vertical movements of the mandible were recorded with an infrared tracking device in humans during biting on two test foods, carrot and cheese. Samples of standard length (2 cm) and width (2 cm) were prepared in three different thicknesses (0.5, 1.0, and 1.5 cm). Nine subjects were asked to perform two types of bite with their incisor teeth. In the first, they cut through the food, then stopped and spat out the pieces (bite alone); in the second, biting was followed by mastication and swallowing (bite+chew). The 12 conditions (thickness x3, food x2, and bite x2) were presented in a random order within each block, and blocks were repeated five times (60 trials per subject). Subjects also estimated the hardness of the samples twice for each condition on visual analogue scales (VAS) 100 mm long. The duration, vertical amplitude, and maximum vertical velocity of the mandible during biting were calculated by computer for the three phases of the movements (opening, and fast and slow closing). Multilevel statistical models were used for data analysis. The estimated hardness scores associated with the first bite of thin carrot (59.0 VAS units) was significantly greater than for cheese (16.8 VAS units). The type of bite had no significant effect on these scores, but the estimate of hardness was significantly greater for the thickest sample (+13.3 VAS units). Food type had its strongest effect on the slow-closing phase. In particular, the peak velocity that followed the fracturing of the food sample was much greater for carrot than for cheese (thin, 34.1 mm.s-1 vs. 26.6 mm.s-1), and the difference between foods increased with thickness. The amplitude of opening was significantly greater for the thickest sample than for the other two. There were no significant relationships between VAS scores and the movement parameters. These results suggest that, when humans bite food: (1) changing the thickness of food has a greater effect on movement parameters than changing from soft to hard food, (2) the parameters of biting change little if biting is followed by mastication, (3) hardness perception is dependent on the thickness of food, (4) hardness perception is not different when food is removed from the mouth than when it is chewed and swallowed, and (5) there is no relationship between any of the parameters of movement that change with food type and the perceived hardness of food.

Pore geometry information via pulsed field gradient NMR.

Studies of echo attenuation at long diffusion times in pulsed field gradient NMR experiments on a variety of rock core samples are interpreted in the light of recent theoretical analysis of the effect of pore geometry and surface relaxation. This study is motivated by the need to test the applicability of that theory to real rock systems.

3D autocorrelation for the determination of large pore sizes.

A data analysis methodology is used to process 3D NMR image data acquired for porous systems. The method extracts the mean size of those repeating elements in the image data which are largely compared with the image voxel dimensions. In this work we extend the two-dimensional (2D) image analysis method described by others to three spatial dimensions (3D). 3D image data were acquired at a magnetic field strength of 7 T using NMR microscopy hardware. The 3D autocorrelation function obtained from the data reveals a characteristic pore size in each dimension.

Strategies for overcoming linewidth limitations in quantitative petrophysical NMR measurements.

The simple pulse-acquire experiment has been used to evaluate the level of accuracy and precision achievable in NMR fluid saturation measurements for a range of rock core samples saturated with either brine or hydrocarbons. For a set of more than 70 cores measured at 0.66 T the mean error in the NMR measurement is only 0.35% porosity when the sample linewidths are less than 50 ppm. However, for a significant portion of cores, those with very broad NMR linewidths (> 50 ppm), difficulties associated with nonuniform excitation are encountered. The magnetic susceptibility difference between pore fluid and rock matrix translates into relatively broad NMR linewidths, and this feature of petrophysical samples is the major difficulty in performing quantitative NMR experiments. Numerical simulations are used to complement the experimental results in order to develop strategies for obtaining accurate NMR results with these difficult samples.